Encapsulation of seeds into capsules of aqueous organic gel, i.e., gel coating of seeds has recently come into use. The gel-coated seeds have an improved rate of germination owing to the water content of the gel coat. The gel coating makes it feasible to mechanize sowing of those seeds which are too small or have a non-spherical shape and are therefore unsuitable to mechanical sowing. Furthermore, various chemicals or fertilizers can be incorporated into the gel coating layer to produce remarkable effects on growth or yield.
Of the conventional gel-coated seeds, those having an aqueous organic gel coat hardened with a metal ion have been widely used because they can be prepared easily and inexpensively and the gel coat gives little adverse influence on germination.
However, the aqueous organic gel coat hardened with a metal ion loses its water content and solidifies during storage, or the gel coat is compellingly dried in order to prevent undesired germination. Such being the case, it is necessary to restore the solidified gel coat on use, for example, on mechanical sowing.
Accordingly, these dried gel capsules have been soaked in water for restoration of the solidified gel coat. However, as the gel capsules swell with water, the surface layer thereof tends to come off, and the capsules lose the surface smoothness. It would follow that the gel capsules undergo increased friction among themselves or with a metallic surface or a resin surface. Thus, gel capsules whose surface layer has fallen off have considerably poor handling properties and are liable to cause clogging during transportation or in a hopper of a seed drill.
Furthermore, the surface layer of gel capsules is relatively hard and strong and has a shape-retaining function. If the surface layer falls off, the strength of the gel capsule is seriously reduced to half or less of the initial strength, and the gel capsules are destroyed very often if handled carelessly after restoration.
When the substance to be encapsulated is a seed, it is required for the gel capsule to be see-through for letting an observer to visually observe the state of the seed. If the surface layer falls off, the gel capsules turn white to have reduced see-through visibility or, in some cases, to completely block visual observation.